This invention relates to a photodetector sensor system which is used to distinguish the motion of specific items relative to a background scene.
For maximum usefulness such a system may need to provide an image of the observed scene in which the background remains stationary, while the motion of an object, or target, is sensed, or to provide an image in which the object, or target, is perceived as stationary with respect to a moving background.
Two lines of prior development pioneered by the assignee of the present application, in the field of photodetector imaging, may usefully be discussed as part of the background information. However, while the usefulness of the present invention will be most fully realized by combining it with those prior developments, such combining is not mandatory. In other words, the present invention has broader potential usefulness.
The first prior line of development by the common assignee is generally called the "Z" technology. This refers to the fact that a focal plane containing a two-dimensional (X and Y) photodetector array is provided on the face of a module, which contains large amounts of electronic processing capacity. The body of the module comprises stacked circuit-carrying layers which lie in planes perpendicular to the focal plane. The dimension of the module perpendicular to the focal plane is its "Z" dimension. Because separate preamplifiers and filters may be included for each detector or picture element, the efficiency of the electronic processing circuitry is dramatically enhanced, and the number of back plane lead-out conductors is drastically reduced.
The second prior art line of development by the common assignee is termed "dynamic stare", because it combines the benefits of staring sensor systems with the benefits of scanning systems. This concept is disclosed and claimed in U.S. Pat. No. 4,675,532, issued June 23, 1987. That patent discusses the usefulness of a combined staring and scanning system in distinguishing a target from its background, both when the target appears to be moving and the background appears to be stationary, and when the background appears to be moving and the target appears to be stationary. In that patent, reference is made to "spatial filters", which respond to the high frequency signals sensed by the scanning motion, and to "temporal filters", which respond to the synchronously demodulated low frequency signals sensed by the same photodetectors. The output signals from the combined system are integrated by storing of repeated pixel signals at a given temporal filter.